The present invention relates to compounds of the Formula I defined below, which inhibit the enzyme glycinamide ribonucleotide formyl transferase (GARFT). The invention also relates to pharmaceutical compositions containing the compounds of the Formula I, to their use to inhibit GARFT and to their use to inhibit the growth and proliferation of the cells of higher organisms or microorganisms such as bacteria, yeast and fungi. The invention also relates to the preparation of these compounds, and to intermediates used in their preparation.
GARFT is a folate dependent enzyme in the de novo purine biosynthesis pathway. This pathway is critical to cell division and proliferation. Shutting down this pathway is known to have an antiproliferative effect, in particular, an antitumor effect. Thus, a number of folate analogs have been synthesized and studied for their ability to inhibit GARFT. A prototypical specific tight-binding inhibitor of GARFT, 5,10-dideazatetrahydrofolic acid (DDATHF), has been reported to show antitumor activity. See F. M. Muggia, "Folate antimetabolites inhibitor to de novo purine synthesis," New Drugs, Concepts and Results in Cancer Chemotherapy, Kluwer Academic Publishers, Boston (1992), 65-87.
The large class of antiproliferative agents includes antimetabolite compounds. A particular subclass of antimetabolites known as antifolates or antifoles are antagonists of the vitamin folic acid. Typically, antifolates closely resemble the structure of folic acid and incorporate the characteristic P-benzoyl glutamate moiety of folic acid. The glutamate moiety of folic acid takes on a double negative charge at physiological pH, and therefore this compound and its analogs have an active energy driven transport system to cross the cell membrane and exert a metabolic effect. Research by a number of investigators has show that folic acid in both its reduced and oxidized forms and its analogs are actively transported into cells by at least two distinct transport mechanisms. These transport proteins are referred to as the reduced folate transport protein, which has a preference for reduced folates but will transport a number of folic acid derivatives. Methotrexate (MTX) is transported via the reduced folate transport system. The other folate transport protein is referred to as the membrane folate binding protein or mFBP, which has a preference for folic acid. See A. C. Antony, "The Biological Chemistry of Folate Receptors," Blood, The Journal of theAmerican Society of Hematology, vol. 79 (1992), 2807-2820.
The anticancer glutamate-containing antifolates used clinically to date, including MTX, enter cells via the reduced folate transport system with one notable exception. 5,10-Dideazatetrahydrofolic acid (DDATHF) is an antitumor GARFT inhibitor currently undergoing clinical study. DDATHF has been shown to be transported into cells via both the reduced folate transport system and the mFBP. See G. Pizzorno et al., "5,10-Dideazatetrahydrofolic Acid (DDATHF) Transport in CCRF-CEM and MA104 Cell Lines," The Journal of Biological Chemistry, vol. 268 (1993), 1017-1023.
It has been suggested that undesirable toxicity, particularly in folate-depleted mammals, is related to the fact that DDATHF, a prior art GARFT inhibitor, has a high affinity for the mFBP, which is unregulated during times of folate deficiency. It has been further suggested that folic acid and other molecules that block the mFBP from transporting other GARFT inhibitors can attenuate the toxicity of such inhibitors. See, e.g., T. Alati et al., "Evaluation of the Mechanism(s) of Inhibition of the Toxicity, But Not the Antitumor Activity of Lometrexol (DDATHF) by Folic Acid," Proceedings of the American Association for Cancer Research, vol. 33 (1992), Abstract 2432, 407; L. L. Habeck et al., "A Novel Class of Monoglutamated Antifolates Exhibits Tight-binding Inhibition of Human Glycinamide Ribonucleotide Formyltransferase and Potent Activity against Solid Tumors," Cancer Research, vol. 54 (1994 ), 1021-1026; and U.S. Pat. No. 5,217,974 to Grindey et al.